This study is a multi-country, multi-center retrospective observational cohort study based on secondary data collected via chart review, with the aim of describing patient characteristics (including relevant comorbidities), monitoring and treatment practices related to Type 1 diabetes mellitus (T1D) progression, and time to T1D progression in participants who received teplizumab as part of Managed Access Programs (MAPs). This study design was chosen in order to gain rapid insight into the current use of teplizumab in clinical practice and the characteristics of patients who received the treatment.